The overall objective is to design, develop and validate stable, implantable telemetry systems for continuous in vivo monitoring (three to twenty-four months) of intracrainial pressure and temperature. Such a system would serve as a valuable, routine, diagnostic instrument for the study of ICP physiology in experimental animals and is ultimately directed towards clinical applications in patients with disorders of ICP regulation. This device is expected to be part of a closed loop system to be used to augment or replace the patient's regulating mechanism. A second proposal emphasizing the basic and clinical physiology is submitted separately. The specific aims of this three year project are: 1) Develop stable, reliable packaging techniques for pressure transducer subassembly to achieve the 2mm Hg/month criteria over a three month to two year implantation period. 2) Develop and evaluate: a) electronic circuits to transmit ICP and temperature information in pulse coded formats for high accuracy; b) techniques to use an analog to digital converter and other large scale intergrated circuits which will operate at microwatt power levels; and c) radio frequency remote controlled command switches which will conserve battery power. 3) Develop and evaluate the total titanium custom flatpack package technique for long-term implantable electronics. 4) Design, develop and evaluate a portable receiver demodulator unit for basic research and clinical application. 5) Evaluate the system in animals in order to characterize its performance, in preparation for clinical adaptation. 6) Carry out physiological study while evaluating the performance of the system, including the study of ICP waveforms specifically in relationship to brain elastance measurements. The lithium battery powered ICP monitoring implant will be 1.4" x 0.75" x 0.25" in size. With a RF command switch, the battery lifetime can be extended from 3 to 24 months. The expected pressure sensitivity is 0.5 mm Hg while the baseline stability is aimed at + 1 mm Hg/month at + 100 mm Hg full scale. The rupture pressure is larger than 2000 mm Hg. This project will be coupled to a physiological study as soon as the initial animal evaluation is completed indicating its usefulness in long term applications.